A new method to study biogeochemical processes in sediments by a percolation technique

Abstract

A device for analysis under simulated natural conditions is described. It continuously exchanges the porewater in undisturbed sediment zones under controlled laboratory conditions. Using this percolation technique, defined aerobic and anaerobic conditions in the sediment and the mean velocity of the porewater can be maintained or varied over extended periods of time. The concentrations of chloride and humic substances in the porewater of an intertidal mudflat sediment were determined continuously in the outflow of the analog model and compared with the results of in situ porewater profile analyses for the same chemicals in the same type of sediment. The pore volume affected by the percolation technique was measured with an amended fluorescent tracer together with chloride as a conservative tracer in the sediment. Vertical gradients of the chemicals in the porewater of an intertidal mudflat sediment were determined using both the percolation and the in situ porewater analysis techniques. Both chloride and humic substances decreased with increasing depth of the sediment. The results obtained using this device indicate differences in the distribution within a sediment layer due to such processes as the accumulation of humic substances in the micropores. In the surface layer, up to 11 times the concentrations of humic substances had accumulated compared to in situ porewater measurements. The application of the percolation technique for the investigation of different biogeochemical processes in sediments is discussed.